18B.5 Health risks of prolonged use of e-cigarettes

Material under review: November 2017     

Suggested citation: Greenhalgh, EM, & Scollo, MM. InDepth 18B: Electronic cigarettes (e-cigarettes). In Scollo, MM and Winstanley, MH [editors]. Tobacco in Australia: Facts and issues. Melbourne: Cancer Council Victoria; 2017. Available from: http://www.tobaccoinaustralia.org.au/chapter-18-harm-reduction/indepth-18b-e-cigarettes

Due to the recency of their introduction to the market, there are no controlled studies on the safety of long-term use of e-cigarettes; however, since e-cigarettes do not generate the smoke that is produced by burning tobacco, their use is generally accepted as likely to be less harmful than smoking conventional cigarettes.1-3 Immediate short term adverse effects of exposure to e-cigarettes are usually mild and transient, and may include nausea, vomiting, mouth and airway irritation, chest pain, and palpitations.4   

E-cigarettes deliver nicotine by creating an aerosol of ultrafine particles, but due to the variability and chemical complexity of fine particles and uncertainty regarding the specific components responsible for toxicity, it is unknown whether e-cigarettes have health effects and toxicity similar to the ambient fine particles generated by conventional cigarette smoke or secondhand smoke.5 This uncertainty is further confounded by the lack of regulation and manufacturing standards, leading to potentially harmful and widely varying ingredients, and significant inconsistency between the labelled content and the actual content and concentrations.6,7 It has become apparent in Australia that some e-cigarettes which are claimed to be free of nicotine, do in fact contain the substance.8 The NSW Ministry of Health tested samples of e-liquids in 2013 and found that 70% of the samples contained high levels of nicotine.9     

Studies on the health risks of using e-cigarettes are limited, and findings to date are inconsistent. Limited results suggest use may have the potential to contribute to non-carcinogenic health risks.10 The 2016 US Surgeon General report on e-cigarette use among youth and young adults concludes that: ‘E-cigarettes can expose users to several chemicals, including nicotine, carbonyl compounds, and volatile organic compounds, known to have adverse health effects. The health effects and potentially harmful doses of heated and aerosolized constituents of e-cigarette liquids, including solvents, flavorants, and toxicants, are not completely understood’.11

18B5.1 Nicotine exposure in pregnancy

Nicotine adversely affects maternal and foetal health during pregnancy, contributing poor outcomes including preterm delivery, still birth, neonatal apnoea, and sudden infant death syndrome.12,13 Nicotine exposure during pregnancy also has lasting adverse consequences for brain and lung development.12 There is currently no clinical knowledge of the efficacy and safety of e-cigarette use in pregnancy, but no amount of nicotine is known to be safe during pregnancy.14 The US Surgeon General noted in 2014 that ‘the evidence is already sufficient to provide appropriately cautious messages to pregnant women and women of reproductive age… about the use of nicotine-containing products such as smokeless tobacco and electronic cigarettes, and newer forms of nicotine-containing tobacco products, as alternatives to smoking.’12 The 2016 report on e-cigarette use concludes that ‘Nicotine can cross the placenta and has known effects on foetal and postnatal development. Therefore, nicotine delivered by e-cigarettes during pregnancy can result in multiple adverse consequences, including sudden infant death syndrome, and could result in altered corpus callosum, deficits in auditory processing, and obesity.’11

18B5.2 Nicotine exposure in adolescence

There is evidence that adolescents who are exposed to nicotine may become addicted more rapidly, and at lower or more intermittent levels of consumption than adults.15-17 Evidence suggests that nicotine exposure during adolescence, a time during which the brain undergoes rapid development, may have a long-term negative impact on higher cognitive function.12,13 The US Surgeon General ’s 2014 report on the health consequences of smoking noted that ‘the evidence is already sufficient to provide appropriately cautious messages to … adolescents about the use of nicotine-containing products such as smokeless tobacco and electronic cigarettes, and newer forms of nicotine-containing tobacco products, as alternatives to smoking'.12 The 2016 report similarly concludes that ‘nicotine exposure during adolescence can cause addiction and can harm the developing adolescent brain’.11  

18B5.3 E-cigarette use and possible cardiovascular disease risk

Conflicting findings have been reported about the potential health effects of e-cigarette use on the cardiovascular system.18-22 The current body of research is limited and short-term, with a lack of high-quality studies and adequate follow-up. Some evidence suggests that e-cigarettes have sympathomimetic effects (i.e., mimicking the action of the sympathetic system) related to nicotine exposure. Limited data suggests that vascular injury may be another concern.23 Given the non-linear relationship between smoking and cardiovascular mortality (i.e., even light smoking can cause significant cardiovascular health effects), reductions in exposure to certain constituents (such as carbonyls and nicotine) through switching from tobacco to e-cigarettes may not result in proportional harm reduction.24 Given the lack of empirical data, the probability of cardiovascular disease risk needs to be assessed from data on toxicity of constituents, levels of exposure, mechanisms, and studies using experimental models. Although the cardiovascular risk is likely much less than that from smoking, e-cigarette emissions of concern for cardiovascular health may include nicotine, oxidizing chemicals, aldehydes (especially acrolein), and particulates.25 Overall, existing evidence is limited and further research is needed to establish the cardiovascular risks of using e-cigarettes long-term.

18B5.4 E-cigarette use and possible cancer risk

The effects of long-term e-cigarette use on cancer risk are unknown. Small amounts of formaldehyde and acetaldehyde, both established carcinogens, have been detected in e-cigarette cartridges.26 In June 2016, the Australian Competition and Consumer Commission commenced action in the Federal court against two online e-cigarette retailers, alleging that their products contained carcinogens and toxic chemicals including formaldehyde, acetaldehyde and acrolein.27 Aerosol produced from some products has also been found to contain traces of carcinogenic nitrosamines,26 and some toxic and potentially carcinogenic metals such as cadmium, nickel, lead,26,28 chromium, manganese, and nickel.28  However, one study noted that the carcinogen levels were nine to 450 times lower than those found in conventional tobacco products.26 A study commissioned by the US Food and Drug Administration in 2009 also detected carcinogens diethylene glycol and nitrosamines at very low levels.29 Some recent studies have suggested that newer products with higher voltage capabilities might produce the same or even higher levels of carcinogenic formaldehyde than tobacco smoke,30,31 but their findings have been challenged.32,33 One review suggests that as propylene glycol in e-liquid is heated and aerosolised, it can be converted to propylene oxide, which is considered possibly carcinogenic to humans.34   

In terms of nicotine exposure, the US Surgeon General’s most recent report concluded that there is insufficient data to conclude that nicotine causes or contributes to cancer.12 However, the International Agency for Research on Cancer Advisory Group has recommended that nicotine’s potential as a carcinogen be reassessed as a matter of high priority, because of increased population exposure to nicotine from e-cigarettes, and recent mechanistic data that ‘suggest an association with DNA damage and other pathways of carcinogenesis.’35

18B5.5 E-cigarette use and possible respiratory disease risk

Other than nicotine, the main ingredient in e-cigarettes is propylene glycol, which is generally considered to be safe for human consumption if swallowed. However, it has not been tested in the manner that e-cigarette use involves; that is, repeated inhalation over a long period of time.36 Frequent exposure to fine and ultrafine particles, such as tobacco smoke, air pollution, and dusts, can contribute to pulmonary and systemic inflammatory processes and increase the risk of cardiovascular and lung diseases.5 The thresholds for human toxicity of potential toxicants in e-cigarette vapour are so far unknown.5 There have been rare reports of exposure causing irritation to the upper and lower respiratory tract mucosa.37 The level of emissions of compounds such as formaldehyde, acetaldehyde, and acrolein appears to increase with the temperature and age (i.e., number of uses) of the device, and for single-coil vs. double-coil e-cigarettes.38 Exposure to metals from e-cigarette vapour, such as nickel, chromium, and titanium, may also pose particular risks to the respiratory system.34

E-cigarettes have been implicated in individual case reports of exogenous lipoid pneumonia, bronchiolitis, acute eosinophilic pneumonia, pneumonia with bilateral pleural effusions, and inhalation injury and suspected acute hypersensitivity pneumonitis.22 Vaping is also associated with increased chronic bronchitic symptoms among adolescents.39 Acute use also leads to lung inflammation,34, 40, 41 which could cause or progress conditions such as COPD and oxidative damage. However, long-term studies are needed to better understand how such acute effects may translate to disease risk.40 A 2017 review concluded that there is a rapidly growing body of evidence that e-cigarette use may have significant pulmonary toxicity. Evidence suggests that e-cigarettes impact multiple regions and functions of the respiratory system, including altering airflow through the conducting airways, increasing oxidative stress, interfering with lung development, and impairing host defence against bacterial and viral pathogens.42

Researchers have also raised concerns regarding the potential harm of inhaled flavourings used in e-cigarettes on the respiratory system.34, 43-47 They suggest that respiratory toxins in the more than 7,000 unique flavourings might pose a threat to the respiratory health of users, particularly as the flavours have primarily been tested in regard to ingestion, rather than inhalation.44 One study found that the concentrations of some flavour chemicals in e-cigarette fluids are sufficiently high for inhalation exposure by vaping to be of toxicological concern, and another found that flavours (along with product type and battery output voltage) significantly affected toxicity of e-cigarette aerosol, with a strawberry-flavoured product being the most cytotoxic.47 Researchers have suggested that regulatory limits should be considered for levels of some of the more worrisome chemicals as well as for total flavour chemical levels, and that ingredients should be labelled.48   

18B5.6 Other health risks  

A number of other potential health risks of e-cigarette use have been identified in recent years. One review notes that exposure to propylene glycol can cause eye irritation, while prolonged or repeated inhalation may affect the central nervous system.34 A 2017 review concluded that e-cigarettes and/or inhaled nicotine along with various flavouring chemicals may contribute to the development of periodontal diseases.49

18B5.7 Exposure to secondhand vapour  

An additional concern regarding the use of e-cigarettes is bystanders’ exposure to second-hand vapour (as exhaled by the user), particularly if the products are used indoors. Several reviews have concluded that e-cigarettes do emit toxicants; however, these emissions are markedly lower than those from conventional cigarettes.50,51 Studies conducted in natural settings are limited and inconsistent,52  although some suggest that indoor use exposes non-users to secondhand aerosol.53 One systematic review has reported that exhaled e-cigarette vapour can contain emissions at a level which affects indoor air quality, including nicotine, particulate matter, glycerine, propylene glycol, formaldehyde, acetaldehyde, polycyclic aromatic hydrocarbons (PAHs) and metals, but mostly to a lesser extent than combustible tobacco products.54

While the health impacts of exposure to second-hand vapour are likely to be less than the impact of combustible tobacco, e-cigarettes do have the capacity to produce environmental pollutants, and in sufficient quantities to potentially harm health.53, 54 Long term studies on the health effects of exposure to second-hand vapour do not yet exist; nor studies on how vapour might impact on the health of vulnerable populations, including children, pregnant women, and people with chronic lung or heart disease.54   

18B5.8 Environmental impact 

Little is known so far regarding the environmental impact of e-cigarettes,i and potential hazards relating to their manufacturing, use and disposal require further investigation. For example, the environmental impact of manufacturing will likely vary based on factory size and the nicotine extracting method used, while disposal of nicotine residue-containing cartridges and battery-containing e-cigarettes represent further potential concerns for the environment.55 There are currently no methods for proper disposal of e-cigarettes or their cartridges.56   


Recent news and research

For recent news items and research on this topic, click here (Last updated March 2018)  


i. Cigarette manufacturing also has a substantial environmental impact (see section 10.4 ), and cigarette butt litter remains a major environmental pollutant that poisons waterways and wildlife and causes bushfires (see section 10.6).  


1. Farsalinos KE and Polosa R. Safety evaluation and risk assessment of electronic cigarettes as tobacco cigarette substitutes: A systematic review. Ther Adv Drug Saf, 2014; 5(2):67–86. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25083263

2. Oh AY and Kacker A. Do electronic cigarettes impart a lower potential disease burden than conventional tobacco cigarettes? Review on e-cigarette vapor versus tobacco smoke. Laryngoscope, 2014; 124(12):2702–6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25302452

3. Goniewicz ML, Gawron M, Smith DM, Peng M, Jacob P, et al. Exposure to nicotine and selected toxicants in cigarette smokers who switched to electronic cigarettes: A longitudinal within-subjects observational study. Nicotine & Tobacco Research, 2016. Available from: http://ntr.oxfordjournals.org/content/early/2016/08/16/ntr.ntw160.abstract

4. Cantrell FL. Adverse effects of e-cigarette exposures. Journal of Community Health, 2014; 39(3):614–6. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24338077

5. Grana R, Benowitz N, and Glantz SA. E-cigarettes: A scientific review. Circulation, 2014; 129(19):1972–86. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24821826

6. Brown CJ and Cheng JM. Electronic cigarettes: Product characterisation and design considerations. Tobacco Control, 2014; 23 Suppl 2(Suppl 2):ii4–10. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24732162

7. Herrington JS, Myers C, and Rigdon A. Analysis of nicotine and impurities in electronic cigarette solutions and vapor. Restek,  2017. Available from: http://www.restek.com/Technical-Resources/Technical-Library/Foods-Flavors-Fragrances/fff_FFAN2127-UNV.

8. Tasmanian Government. Warning on e-cigarettes. 2014. Available from: https://www.dhhs.tas.gov.au/news/2014/warning_on_e-cigarettes

9. NSW Health. NSW health alert—warning on e-liquids. 2013. Available from:http://www.health.nsw.gov.au/news/Pages/20131023_00.aspx

10. Zulkifli A, Abidin EZ, Abidin NZ, Amer Nordin AS, Praveena SM, et al. Electronic cigarettes: A systematic review of available studies on health risk assessment. Reviews on Environmental Health, 2016. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27101543

11. US Department of Health and Human Services. E-cigarette use among youth and young adults. A report of the Surgeon General. Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2016. Available from: https://www.cdc.gov/tobacco/data_statistics/sgr/e-cigarettes/index.htm.

12. U.S. Department of Health and Human Services. The health consequences of smoking: 50 years of progress. A Report of the Surgeon General, Atlanta, GA: US Department of Health and Human Services, Centers for Disease Control and Prevention, National Center for Chronic Disease Prevention and Health Promotion, Office on Smoking and Health, 2014. Available from: http://www.surgeongeneral.gov/library/reports/50-years-of-progress/full-report.pdf.

13. England LJ, Bunnell RE, Pechacek TF, Tong VT, and McAfee TA. Nicotine and the developing human: A neglected element in the electronic cigarette debate. American Journal of Preventive Medicine, 2015; 49(2):286–93. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25794473

14. Suter MA, Mastrobattista J, Sachs M, and Aagaard K. Is there evidence for potential harm of electronic cigarette use in pregnancy? Birth Defects Res A Clin Mol Teratol, 2015; 103(3):186–95. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25366492

15. McNeill AD. The development of dependence on smoking in children. British Journal of Addiction, 1991; 86(5):589–92. Available from: https://www.ncbi.nlm.nih.gov/pubmed/1859924

16. O'Loughlin J, DiFranza J, Tyndale RF, Meshefedjian G, McMillan-Davey E, et al. Nicotine-dependence symptoms are associated with smoking frequency in adolescents. American Journal of Preventive Medicine, 2003; 25(3):219–25. Available from: https://www.ncbi.nlm.nih.gov/pubmed/14507528

17. Doubeni CA, Reed G, and Difranza JR. Early course of nicotine dependence in adolescent smokers. Pediatrics, 2010; 125(6):1127–33. Available from: https://www.ncbi.nlm.nih.gov/pubmed/20439592

18. Lippi G, Favaloro EJ, Meschi T, Mattiuzzi C, Borghi L, et al. E-cigarettes and cardiovascular risk: Beyond science and mysticism. Seminars in Thrombosis and Hemostasis, 2014; 40(1):60–5. Available from: https://www.ocf.berkeley.edu/~dshuster/e-Cigarettes/Lippi_2014.pdf

19. Farsalinos KE, Romagna G, and Le Houezec J. Comment on "e-cigarettes and cardiovascular risk: Beyond science and mysticism". Semin Thromb Hemost, 2014; 40(4):517–8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24802086

20. Callahan-Lyon P. Electronic cigarettes: Human health effects. Tobacco Control, 2014; 23 Suppl 2:ii36–40. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24732161

21. Vlachopoulos C, Ioakeimidis N, Abdelrasoul M, Terentes-Printzios D, Georgakopoulos C, et al. Electronic cigarette smoking increases aortic stiffness and blood pressure in young smokers. Journal of the American College of Cardiology, 2016; 67(23):2802–03. Available from: http://www.sciencedirect.com/science/article/pii/S0735109716326559

22. Hua M and Talbot P. Potential health effects of electronic cigarettes: A systematic review of case reports. Preventive Medicine Reports, 2016; 4:169–78. Available from: http://www.ncbi.nlm.nih.gov/pmc/articles/PMC4929082/

23. Nelluri B, Murphy K, Mookadam F, and Mookadam M. The current literature regarding the cardiovascular effects of electronic cigarettes. Future Cardiology, 2016; 12(2):167–79. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26916427

24. Bhatnagar A. E-cigarettes and cardiovascular disease risk: Evaluation of evidence, policy implications, and recommendations. Current Cardiovascular Risk Reports, 2016; 10(7):1–10. Available from: http://dx.doi.org/10.1007/s12170-016-0505-6

25. Benowitz NL and Fraiman JB. Cardiovascular effects of electronic cigarettes. Nature Reviews. Cardiology, 2017; 14(8):447–56. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28332500

26. Goniewicz ML, Knysak J, Gawron M, Kosmider L, Sobczak A, et al. Levels of selected carcinogens and toxicants in vapour from electronic cigarettes. Tobacco Control, 2014; 23(2):133–9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/23467656

27. Australian Competition & Consumer Commission. Accc takes action against e-cigarette suppliers for alleged misleading “no toxic chemicals” claims. 2016. Available from: http://www.accc.gov.au/media-release/accc-takes-action-against-e-cigarette-suppliers-for-alleged-misleading-%E2%80%9Cno-toxic-chemicals%E2%80%9D-claims

28. Hess CA, Olmedo P, Navas-Acien A, Goessler W, Cohen JE, et al. E-cigarettes as a source of toxic and potentially carcinogenic metals. Environmental Research, 2017; 152:221–5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27810679

29. US Food and Drug Administration (FDA). Evaluation of e-cigarettes (DPATR-FY-09-23), 2009. Available from: http://www.fda.gov/downloads/Drugs/SCienceResearch/UCM173250.pdf

30. Jensen RP, Luo W, Pankow JF, Strongin RM, and Peyton DH. Hidden formaldehyde in e-cigarette aerosols. New England Journal of Medicine, 2015; 372(4):392–4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25607446

31. Kosmider L, Sobczak A, Fik M, Knysak J, Zaciera M, et al. Carbonyl compounds in electronic cigarette vapors: Effects of nicotine solvent and battery output voltage. Nicotine & Tobacco Research, 2014; 16(10):1319–26. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24832759

32. Bates C. Spreading fear and confusion with misleading formaldehyde studies. 2015. Available from: http://www.clivebates.com/?p=2706

33. Farsalinos K. The deception of measuring formaldehyde in e-cigarette aerosol: The difference between laboratory measurements and true exposure. E-cigarette Research, 2015. Available from: http://www.ecigarette-research.org/research/index.php/whats-new/whatsnew-2015/191-form-nejm

34. Kim KH, Kabir E, and Jahan SA. Review of electronic cigarettes as tobacco cigarette substitutes: Their potential human health impact. Journal of Environmental Science and Health. Part C, Environmental Carcinogenesis & Ecotoxicology Reviews, 2016; 34(4):262–75. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27635466

35. Straif K, Loomis D, Guyton K, Grosse Y, Lauby-Secretan B, et al. Future priorities for the IARC monographs. The Lancet Oncology, 2014; 15(7):683–4. Available from: http://dx.doi.org/10.1016/S1470-2045(14)70168-8

36. Britton J and Bogdanovica I. Electronic cigarettes: A report commissioned by Public Health England.  2014. Available from: https://www.gov.uk/government/uploads/system/uploads/attachment_data/file/311887/Ecigarettes_report.pdf.

37. Orellana-Barrios MA, Payne D, Mulkey Z, and Nugent K. Electronic cigarettes-a narrative review for clinicians. American Journal of Medicine, 2015; 128(7):674–81. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25731134

38. Sleiman M, Logue JM, Montesinos VN, Russell ML, Litter MI, et al. Emissions from electronic cigarettes: Key parameters affecting the release of harmful chemicals. Environmental Science & Technology, 2016; 50(17):9644–51. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27461870

39. McConnell R, Barrington-Trimis JL, Wang K, Urman R, Hong H, et al. Electronic cigarette use and respiratory symptoms in adolescents. American Journal of Respiratory and Critical Care Medicine, 2017; 195(8):1043–9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27806211

40. Zucchet A and Schmaltz G. Electronic cigarettes—a review of the physiological health effects. Facets, 2017. Available from: http://facetsjournal.com/article/facets-2017-0014/

41. Shields PG, Berman M, Brasky TM, Freudenheim JL, Mathe E, et al. A review of pulmonary toxicity of electronic cigarettes in the context of smoking: A focus on inflammation. Cancer Epidemiology, Biomarkers & Prevention, 2017; 26(8):1175–91. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28642230

42. Chun LF, Moazed F, Calfee CS, Matthay MA, and Gotts JE. Pulmonary toxicity of e-cigarettes. American Journal of Physiology - Lung Cellular and Molecular Physiology, 2017; 313(2):L193–L206. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28522559

43. Martin EM, Clapp PW, Rebuli ME, Pawlak EA, Glista-Baker E, et al. E-cigarette use results in suppression of immune and inflammatory-response genes in nasal epithelial cells similar to cigarette smoke. American Journal of Physiology - Lung Cellular and Molecular Physiology, 2016; 311(1):L135–44. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27288488

44. Barrington-Trimis JL, Samet JM, and McConnell R. Flavorings in electronic cigarettes: An unrecognized respiratory health hazard? Journal of the American Medical Association, 2014; 312(23):2493–4. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25383564

45. Allen JG, Flanigan SS, LeBlanc M, Vallarino J, MacNaughton P, et al. Flavoring chemicals in e-cigarettes: Diacetyl, 2,3-pentanedione, and acetoin in a sample of 51 products, including fruit-, candy-, and cocktail-flavored e-cigarettes. Environmental Health Perspectives, 2016; 124(6):733–9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26642857

46. Rowell TR, Lee S, and Tarran R. Select e-cigarette flavors alter calcium signaling, cell viability and proliferation in lung epithelia. American Thoracic Society International Conference, 2015. Available from: http://www.atsjournals.org/doi/abs/10.1164/ajrccm-conference.2015.191.1_MeetingAbstracts.A2896

47. Leigh NJ, Lawton RI, Hershberger PA, and Goniewicz ML. Flavourings significantly affect inhalation toxicity of aerosol generated from electronic nicotine delivery systems (ends). Tobacco Control, 2016; 25(Suppl 2):ii81–ii7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27633767

48. Tierney PA, Karpinski CD, Brown JE, Luo W, and Pankow JF. Flavour chemicals in electronic cigarette fluids. Tobacco Control, 2016; 25(e1):e10–5. Available from: https://www.ncbi.nlm.nih.gov/pubmed/25877377

49. Javed F, Kellesarian SV, Sundar IK, Romanos GE, and Rahman I. Recent updates on electronic cigarette aerosol and inhaled nicotine effects on periodontal and pulmonary tissues. Oral Dis, 2017; 23(8):1052–7. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28168771

50. Fernandez E, Ballbe M, Sureda X, Fu M, Salto E, et al. Particulate matter from electronic cigarettes and conventional cigarettes: A systematic review and observational study. Current Environmental Health Reports, 2015; 2(4):423–9. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26452675

51. Burstyn I. Peering through the mist: Systematic review of what the chemistry of contaminants in electronic cigarettes tells us about health risks. BMC Public Health, 2014; 14(1):18. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24406205

52. Zainol Abidin N, Zainal Abidin E, Zulkifli A, Karuppiah K, Syed Ismail SN, et al. Electronic cigarettes and indoor air quality: A review of studies using human volunteers. Reviews on Environmental Health, 2017; 32(3):235–44. Available from: https://www.ncbi.nlm.nih.gov/pubmed/28107173

53. Soule EK, Maloney SF, Spindle TR, Rudy AK, Hiler MM, et al. Electronic cigarette use and indoor air quality in a natural setting. Tobacco Control, 2017; 26(1):109–12. Available from: https://www.ncbi.nlm.nih.gov/pubmed/26880745

54. Hess IM, Lachireddy K, and Capon A. A systematic review of the health risks from passive exposure to electronic cigarette vapour. Public Health Research and Practice, 2016; 26(2):e2621617. Available from: https://www.ncbi.nlm.nih.gov/pubmed/27734060

55. Chang H. Research gaps related to the environmental impacts of electronic cigarettes. Tobacco Control, 2014; 23 Suppl 2(Suppl 2):ii54–8. Available from: https://www.ncbi.nlm.nih.gov/pubmed/24732165

56. National Institure for Health and Care Excellence. Tobacco: Harm-reduction approaches to smoking. NICE Public Health Guidance 45, 2013. Available from: http://www.nice.org.uk/guidance/ph45/resources/guidance-tobacco-harmreduction-approaches-to-smoking-pdf


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